Heat flows from a warm object to a cool object by way of conduction, convection, and radiation. Conduction is transfer of heat through physical objects, such as a thermometer under your tongue. Convection is transfer of heat through a fluid, such as an ice cube cooling a glass of water. Radiation is the transfer of heat through free space, such as warming your hands by a fire. Such properties are often optimized in materials used to construct buildings and homes to make the buildings comfortable and more energy efficient.
On the other hand, these thermal properties are less often optimized in materials used to fabricate outdoor walking surfaces, such as driveways, sidewalks, patios, and the like. For example, swimming pools are typically surrounded by ceramic tiles or concrete. After exposure to direct sunlight, these surfaces can become so hot to be uncomfortable to the touch. This situation is commonly experienced by an individual who must soft step across the tile or concrete surface to move about the pool area with bare feet.
These walking surfaces are believed to be uncomfortably hot to touch because of the combination of high thermal mass, low emissivity, and low thermal conductivity. Thermal mass is the ability of a material to store heat. Emissivity is the ability of a surface to emit or give off heat. Thermal conductivity is the ability of a material to transfer energy or heat. As a result, the typical material used to surround a pool (i.e., ceramic tiles or concrete) easily store heat energy from the sun, and lack the ability to quickly radiate this stored energy every quickly, and easily transfer it to the ground underneath. As such, upon extended exposure to direct sun-light, these materials will be uncomfortably hot to the touch.
Insulating properties have been addressed by blending into materials a small quantity of hollow glass microspheres. For example, insulating paint and coatings have been prepared by blending about 6.5 percent to about 16.5 percent microspheres to form an insulating paint or an insulating thermal coating. (See, e.g., U.S. Pat. Nos. 4,623,390 and 4,332,618.) In another example, an insulating elastomeric roof coating is prepared by blending about 6.2 percent glass shells into a polymer and resin mixture. (See, e.g., U.S. Pat. No. 5,713,974). These examples blend a small quantity of microspheres (i.e., less than about 16.5 percent) into a base material to obtain the desired insulating properties. Such low level microsphere formulations, however, do not necessarily provide a surface that is comfortable to touch after exposure to an energy source because optimization of a material's insulating characteristics is distinct from improving its surface thermal properties.
It is also known to blend higher density additives (i.e., cellulose fibers or glass fibers) and lower density additives (i.e., microballoons) into resin systems as fillers and thickeners to generally improve the strength of the resin system. Typically, these applications only include about 4 percent to about 60 percent filler if using the high density additive or about 20 percent to about 40 percent if using the low density additive.
Accordingly, there is a desire for a material that can be exposed to an energy source, such as direct sun light, and retain the ability to be comfortably touched even after extended exposure to the energy source. It also is desired for the material to have sufficient structural integrity to support waling on it and use of furniture without becoming damaged.